Intersperse text and images

## What problem does this solve or what need does it fill?

Allow images to be interspersed with wrapped text as though the images are glyphs.

## What solution would you like?

An `ImageSpan` component containing the image handle and color that can be added as a child to text nodes in the same way that `TextSpan`s can be.

## What alternative(s) have you considered?

You can do a manual text layout by making each word into a distinct `Text` node with flex wrap. Then you can just add `ImageNode`s amongst the text nodes. It's extremely awkward and inefficient though.

## Additional context

Maybe we could use a "font" with images as glyphs. I'm not sure what cosmic text supports.

Start by tracing Bevy's existing text-node and TextSpan implementation, then investigate how cosmic text could represent inline images. Done means an ImageSpan can carry an image handle and color and be added among text spans so wrapped text and images flow together.

Written by the indexing model from the issue text.